Background: Psoriasis is a chronic, inflammatory, and hyperproliferative disease. Recently there have been studies regarding increases in the levels of NO in inflammatory dermatoses including psoriasis Objective: The aim of this study was to measure serum nitric oxide (NO) levels in patients with active psoriasis, to correlate these levels with duration and severity of the disease and compare them with those in normal individuals. Patients and Methods: In this study, 40 patients with psoriasis were scored with PASI score and the levels of serum nitric oxide were detected by Greiss method. The results were compared with forty (40) healthy volunteers. The relation of the results with the clinical severity, duration of the disease as well as duration of the current episode were also evaluated. Results: Out of the 40 patients with psoriasis 30 (75%) presented with chronic plaque psoriasis, 7 (17.5%) presented with acute attack of guttate psoriasis, 1 (2.5%) patient with erythrodermic psoriasis, 1 (2.5%) with pustular psoriasis and 1 (2.5%) with scalp psoriasis. The duration of the disease ranged between 6 months to 25 years while the PASI score ranged between (1.60- 49.50). The mean NO level in psoriatic group was 125.0μ mol/L with SD 38.77, while in the control group it was 42.37μ mol/L with SD 23.57. The difference was statistically significant (p